1. Field of the Invention
This invention relates to propylene-alpha-olefin copolymer compositions. In one aspect the invention relates to foamable propylene-α-olefin copolymer compositions while in another aspect, the invention relates to a process of foaming such compositions under restricted conditions. In still another aspect the invention relates to compositions designed for use in the manufacture of artificial leather.
2. Description of the Related Art
Propylene-α-olefin copolymers can be successfully used in existing polyvinyl chloride (PVC) artificial leather production lines, and to prepare foamed synthetic leathers with satisfactory mechanical and haptic performance for artificial leather markets such as sporting goods (bags, gloves, tarpaulin and balls etc.) and shoe uppers. Representative of this technology is PCT/US2010/035256.
Production of artificial leather is a continuous process, and certain steps such as compounding, calendaring and lamination, require a processing temperature of about 150° C., to prevent pre-foaming of blowing agents, followed by foaming at a temperature of about 220° C. for 30 to 200 seconds (s) (the “foaming window”). Although numerous propylene-α-olefin copolymer formulations have been developed, some exhibit a narrower foaming window (less than (<) 120 s at 220° C.) than required for existing PVC lines (30-200 s at 220° C.), i.e., the foam structure is destroyed after a longer time of foaming (greater than (>) 120 s) at a foaming temperature of 220° C. Incorporation of 20-50 weight percent (wt %) or more styrene-ethylene-butylene-styrene (SEBS) block elastomer into the formulation provides the desired foaming performance, including the required foaming window and final product performance, but the costs of the operation are greatly increased.
As such an interest exists in developing a composition for artificial leather applications which has good foam stability, is cost effective (does not require SEBS or use less amount of SEBS), and offers a wider foaming window (>120 s at 220° C.) without sacrificing the processability for compounding, calendaring and lamination, as well as performance of the final products.